Processing plants use control valves in a wide variety of applications such as, for example, controlling product flow in a food processing plant, maintaining fluid levels in large tank farms, etc. Automated control valves are used to manage the product flow or to maintain the fluid levels by functioning like a variable passage. The amount of fluid flowing through a valve body of the automated control valve can be accurately controlled by precise movement of a valve member (e.g., a plug). In some control valves, the control valve (e.g., a sliding valve stem valve) may include a metal valve stem connected via threads to a threaded opening of a metal valve member so that the metal valve stem is oriented substantially perpendicular to the metal valve member. The metal valve stem may be fixed to the metal valve member by welding together the metal valve stem and the metal valve member. However, the valve stem and valve member cannot be welded together if either the valve stem or the valve member are made of a non-weldable material, or if the filler material is incompatible with the base material of the valve stem or the valve plug. For example, the valve stem may be made of a weldable material such as, for example, 316 strain-hardened stainless steel and the valve member may be made of a non-weldable cast material such as, for example, Monel®. Alternatively, the valve stem may be secured to the valve member by using a drive pin. However, connecting the valve stem to the valve member by using a drive pin can cause misalignment between the valve stem and the valve member and affect the integrity of the valve member.
The combination of a metal valve stem and a metal or non-metallic valve member such as, for example, a ceramic valve member, may be utilized for certain processes. During the operation of the control valve, tensile forces will be exerted by the threads of the metal valve stem on the threads of the ceramic valve member. The engagement of the threads of the metal valve stem with the threads of the ceramic valve member can result in damage to the ceramic valve member.